The design of modern gears is based on the original design of the wheel, dating back millennia. The design of the wheel greatly reduces friction by allowing the wheel to rotate with respect to another surface (i.e., roll over a supporting ground surface). A wheel includes a circular outer rim designed to rotate and an axle to provide support and orientation to the wheel. Conventional wheel design includes a central hub at the center of the circular wheel. The central hub is coupled with the axle. The axle may either be fixed with the wheel, allowing the wheel to rotate with the axle, or the wheel may be rotatably coupled with the axle, allowing the wheel to rotate about the axle while the axle remains fixed. A webbing or a plurality of spokes extend from the central hub to support the circular outer rim of the wheel.
All of the loading and impacts imparted onto the wheel are transmitted to the axle in the form of shear loads, lateral loads, and bending moments. As a result, desirable axle and central hub properties include high strength, impact resistance, high bending strength, and high fracture toughness. Depending on the application, central hubs, webbings and axles are typically heavily reinforced and made from durable materials (e.g., steel) so that they can reliably withstand loads applied to the circular outer rim or other portions of the wheel.
Another element of wheel design is lubrication of the axle. Conventionally, the central hub rotates on an outer surface of the axle. An oil-based or other loss-type lubricant can be applied to lubricate the axle and the central hub. The typical lubricant slowly seeps from the wheel and/or the material integrity of the lubricant degrades over time, creating the regular need for re-application of the lubricant. Re-application of the lubricant often require stopping of the wheel and any associated machinery followed by manual disassembly and reassembly of the wheel after the lubricant is re-applied. Despite these drawbacks and the ongoing expense of re-application, lubrication is necessary in many wheels because it reduces friction and prolongs service life of both the wheel and axle.
A conventional axle is much smaller in diameter than the rim of the wheel. As a result, the linear velocity of the central hub rotating about the axle is much smaller than the linear velocity of the outer rim with rotating with respect to the axle. Mounting the central hub on the axle, instead of mounting the rim on the axle, thus minimizes wear between the axle and the wheel. It also increases effectiveness of the lubricant by generating less heat, which can degrade the material integrity of the lubricant. Thus, another desirable axle property is a smaller-diameter shaft because it yields less wear from friction and requires less material. As materials and manufacturing techniques improved over time, axles became both smaller and stronger following conventional wheel design principles. Accordingly, the conventional axle is many times smaller than the wheel it supports.
One implementation of a wheel is a gear drive system or geartrain such as those found in a transmission or gearbox. A gearbox is generally used to provide speed and torque conversions from a rotating input shaft to a rotating output shaft. For example, a step-down gearbox can include a geartrain for lowering the rotational speed of an input shaft and increasing the output torque at an output shaft; a step-up gearbox can include a geartrain for increasing the rotational speed of an input shaft which decreases the torque at an output shaft. Some known gearboxes rely on a series of meshed gears (e.g., spur, helical, herringbone, or compound gears) that include gear teeth mounted on an outer rim supported by a webbing and a hub mounted on a smaller-diameter or conventional shaft or axle. By varying the sizes of the gears within the series of meshed gears and/or using compound gears of varying sizes, a mechanical advantage can be obtained between an input side and an output side of the gearbox.
One type of geartrain that uses gears such as those noted above is the valvetrain system of an internal combustion engine (ICE). The valvetrain system of an ICE performs an important function in the operation of an engine and can affect performance of the engine. In many current commercial engines, the valvetrain system includes one or more camshafts driving one or more intake valves and one or more exhaust valves for each cylinder. Generally, in a four-stroke engine having an intake stroke, a compression stroke, a power stroke and an exhaust stroke, the intake valves open during the intake stroke and close during the compression stroke and the exhaust valves open during the exhaust stroke and close during the intake stroke. The intake valves control the ingress of combustion reactants, such as air and/or fuel, into the combustion chamber and exhaust valves control the egress of combustion products, such as H2O, CO, CO2, NOx, and unburned hydrocarbons out of the combustion chamber.
The timing and movement of the intake valve and exhaust valve can play a significant role in the overall performance of an engine, such as the volumetric efficiency and maximum engine speed. Accordingly, precise synchronization of the piston and crankshaft movements with the valve and camshaft movements is of paramount importance to an engine. The camshafts are generally configured to control the timing and movement of the valves and are generally timed in accordance with movement of the pistons by means of a crankshaft coupled with the camshafts through a drivetrain. Existing drivetrains include serpentine belts, chains, and geartrains which transmit rotational energy from the crankshaft of the engine to the camshafts.